1. Field of the Invention
The present invention relates to pressure regulation apparatus and more particularly concerns a novel safety apparatus for use in beverage dispensing applications wherein a source of high pressure gas is interconnected with a container containing the beverage to be dispensed, such as beer or soft drinks, and gases under pressure are introduced into the container to cause the dispensing of the beverage through a fluid outlet from the container.
2. Background of the Invention
Typically, dispensing systems for carbonated beverages use carbon dioxide gas as a pressurization media for dispensing the beverage. This is done for a variety of reasons. First of all, the system requires some sort of gas pressure applied to the reservoir of beverage in order to "push" the beverage out through the container outlet, or dispensing faucet. In addition, since the beverages are already carbonated, the carbonation level, and accordingly, the quality of the product, is maintained by keeping a fixed level of carbon dioxide gas pressure applied to the free surface of the light beverage.
Generally the carbon dioxide used as the dispensing medium is pressurized to its "critical pressure" at which point it becomes liquid and can be stored in that state with great density inside a heavy-walled, high-pressure, gas cylinder. Nearly all industrial gases are stored in heavy-walled pressure cylinders and generally are transported and dispensed without catastrophic incident. This is because in most industrial uses the gasses are dispensed through various types of flow and pressure regulators to atmosphere for welding, breathing, or whatever. However, in the case of beverage dispensing, the gases are dispensed into another pressure vessel which, if over-pressurized, becomes explosive and can do great damage and can cause serious injury and even death.
In the past, in order to avoid over-pressurization in the normal operation of beverage dispensing systems, a pressure reducing regulator is installed on the CO.sub.2 gas cylinder or bottle to reduce the pressure from its nominal level of, say, 1000 pounds per square inch (psi), to the dispensing pressure required for the particular beverage. In beer, for example, the dispensing pressure is normally about 15 pounds per square inch gauge (psig). It has been normal practice to install a single pressure reducing regulator at the bottle and then transport the gas at the reduced pressure to the containers or kegs containing the liquid through plastic hoses having a wall thickness of about 1/8 inch. The pressurization limit of such hose is variable and may range from about 450 psi instantaneous gauge pressure down to some 60 or 80 psi continuously applied pressure over a time span of 20 or 30 minutes. In short, the pressure retention capacity of the plastic hose, or of any other plastic material, is time-dependent. Unfortunately, the metal pressure vessel containing the beverage to be dispensed has a specific yield point that is instantaneously effective and causes the container to catastrophically rupture at a lower instantaneously applied pressure than the hose itself. The net result is that the failure of the pressure regulator can cause the pressure vessel, or beverage container, to explosively rupture and cause great damage. Unfortunately, catastrophic over-pressurization frequently occurs at the time of connection of the source of gas when someone is standing nearby and, therefore, frequently results in death or dismemberment.
A standard commercially available pressure reducing regulator which has been attached to a high pressure source of liquified gas, like any other mechanical device, is going to fail at some point in time. It is not so much a question of whether the device will fail, but rather when and how it will fail. The regulator can, of course, fail in the closed position, meaning that no gas can be transported through the device to, or toward, the pressure vessel or beverage container. That mode of failure, unfortunately, is very infrequent. The more frequent mode of failure is the over-pressurization failure, which is the catastrophically dangerous mode of failure. The high pressure, or over pressure failure mode can be characterized as a "creeping" failure or an "instantaneous" high-pressure failure. Either mode of high-pressure failure can cause the beverage vessel to rupture explosively.
In light of the failure propensity of commercial regulators, manufacturers of the regulators have recommended the installation of "relief valves" somewhere downstream in the system. Further, in various attempts at avoiding liability and "achieving safety", various organizations "require" the installation of the relief valve in the coupling device in order that it is always present in the system. However, the existence of the "safety relief valve" at such a location is absolutely a waste of time. In the first place, there is no way to functionally test the device to see whether or not it is working, that is, to see whether or not it lifts at the prescribed pressure. Secondly, it can be, and frequently is, contaminated by product exposure and has glued itself shut. Third, because of its location (integral with the tapping device) it is too small in size to expel the gas from the system at the same rate that it is flowing into the system. Accordingly, the pressure continues to build inside the pressure vessel without regard for the presence of the device. Fourth, because of the nature of the CO.sub.2 gas, and its propensity for freezing, the relief device, if it actuates at all, will promptly freeze the escape port closed in a few seconds. When this occurs, the continued discharge of the gas and the pressure inside the pressure vessel will soon build to an equilibrium level with the pressure inside the bottle. It requires no detailed analysis to conclude that when using liquified gas storage one always has pressures in the range of 800 psi to 1800 psi, or higher, at the pressure source. For the reasons previously discussed it must be concluded that there is only one element in the typical prior art system which can cause, or allow, an over-pressurization circumstance and that item is the Pressure Reducing Regulator. A failure of the Pressure Reducing Regulator, whether induced or accidental, can allow the high pressure which is always available at the source to feed through into the system. Every beer keg or pressure vessel that has ever been manufactured can be explosively ruptured if exposed to the maximum pressure available in the normally used high pressure gas sources. Accordingly, since commercial pressure reducing regulators will fail as a function of time, the prior art dispensing systems comprise fused "time bombs" just waiting to go off.
As will become apparent from the discussion which follows, the method and apparatus of the present invention overcomes the drawbacks of the prior art and, for the first time, provides an absolutely safe apparatus for use in the dispensing of beverages in systems using high pressure gas sources.
Basically the apparatus of the invention precludes catastrophic failure by providing two redundant regulators in series installation and, at the same time, providing means for continuously monitoring the system in a manner which will give a positive indication of the failure of one of the regulators. As a back-up to the redundant regulators, a frangible burst disc is strategically placed within the system to positively preclude over-pressurization of the system. Further, the unique method and apparatus of the invention insures that if one regulator should fail the system must be shut down for corrective action. Finally, since one of the major causes of regulator failure is contamination with dried beverage product, the system also includes means to positively preclude the exposure of the redundant regulator devices to the beverage product.